Conventionally, as non-invasion type blood circulation measuring equipment, various kinds of blood pressure measuring apparatuses constructed so that Korotkoff's sounds and fluctuations of pulse wave pressure, which are generated by changing the cuff pressure, are detected in a state that a cuff is wound on an arm of a patient and is inflated by supplying air, etc. so as to tighten the arm with pressure applied to surface of the body of a patient have been used. In these blood pressure measuring apparatuses, there are many cases where they display the systolic blood pressure, mean blood pressure, diastolic blood pressure, and pulse rate of a patient, and they are used to presume the blood circulation of the patient with these values.
In a method for measuring the blood pressure value on the basis of Korotkoff's sounds detected by a cuff, since the Korotkoff's sounds are small and simultaneously the frequency band of the corresponding Korotkoff's sounds is in such a range where Korotkoff's sounds are liable to be influenced by environmental noise, an erroneous detection is apt to occur, and since the attenuation amounts of the sound waves are greatly different, depending upon a detection part and/or the thickness of the upper part tissue, there occurs such a problem where the detection error becomes large and the repeatability thereof is bad.
Therefore, recently, an oscillometric method in which the blood pressure is directly detected from changes of a cuff pressure has been utilized. According to this method, pulse waves of a patient which are overlapped on the cuff pressure are extracted from detection signals obtained by a detection means such as a pressure sensor, etc., the pulse wave amplitude values are read, and the blood pressure value is determined by reference to the cuff pressure value obtained by the maximum value of the pulse wave amplitudes. In this case, the cuff pressure value at the point when the pulse wave amplitude shows the maximum value is displayed as a mean blood pressure value, the cuff pressure value at the point when the pulse wave amplitude multiplied by an appointed ratio for the corresponding maximum value is obtained at a higher pressure side of the cuff pressure than the maximum value is displayed as the systolic blood pressure value, and the cuff pressure value at the point when the amplitude value multiplied by an appointed ratio for the corresponding maximum value is obtained at a lower pressure side of the cuff pressure than the maximum value is displayed as the diastolic blood pressure.
In a blood pressure measurement by this oscillometric method, it is possible to utilize a high sensitivity pressure sensor, and a highly accurate and highly repeatability measurement, which is hardly influenced by environmental noise and environmental vibrations, is enabled since the detection signals thereof are in a low frequency band zone.
In almost all conventional blood pressure measuring apparatuses, only the systolic blood pressure value, mean blood pressure value, diastolic blood pressure value, and pulse rate are detected. Although these blood pressure values are influenced by the cardiac output conditions and conditions of arteriosclerosis, they are determined by various factors in a living body. Therefore, it is impossible to accurately grasp the cardiovascular conditions of a patient by merely checking the blood pressure values. Furthermore, it is impossible to correctly evaluate the meaning of the blood pressure values themselves unless there is some information other than the blood pressure values regarding the cardiovascular system of a patient. Therefore, it is impossible to make a correct diagnosis on the basis of only the blood pressure values obtained by any conventional sphygmomanometer, whereby it is real that the blood pressure values are regarded as mere references for medical diagnoses.
In the product process of a measuring apparatus in which an oscillometric method is used, the blood pressure values secured by a direct method in which a catheter is inserted into a blood vessel are compared in advance with the blood pressure values obtained by the measuring apparatus itself, calculation parameters of blood pressure values in the measuring apparatus are determined so that the blood pressure values obtained by the apparatus show the values identical to those secured by the direct method, and the measurement values secured by the measuring apparatus become as accurate as possible. However, various situations are considered in the cardiovascular system of a patient even in cases where the blood pressure values show almost the same values as those secured by the direct method. Still furthermore, even though a measurement apparatus is adjusted to be strictly accurate, there are cases where the blood pressure values secured by the measurement apparatus are greatly different from those secured by the direct method in some conditions of the cardiovascular system.